1. Field of the Invention
The present invention relates to sheet handling devices and more particularly to sheet handling devices employing pneumatic means for gripping and feeding the sheets.
2. The Prior Art
It is conventional to employ a suction means for gripping and feeding sheets in apparatus for processing sheets such as die cutting machines, printing presses and the like. In one arrangement, a movable suction plate is employed formed generally of a flat plate having apertures therein connected with a vacuum source, adapted for engaging and drawing a sheet down into register with the plate. Such a mechanism works satisfactorily as long as the sheets are planar, but when the sheets are curved or warped, many of the apertures do not come into engagement with the sheet, with the result that the sheet is not firmly gripped by the movable plate.
An improvement on such a feed device incorporates one or more telescopic suction members which are adapted to be extended to the location of the sheet and then to draw the sheet down into engagement with a support plate, thereby aligning the sheet in the proper plane for feeding. Even though this is an improvement over the suction plate alone, nevertheless even the telescopic members are not effective when a sheet has a pronounced curvature, as the plane of the suction members, even though extended, forms an angle with the surface of the sheet so that the aperture of the suction member is not effectively blocked from the atmosphere. It is accordingly desirable to provide an alternative arrangement which is not subject to these disadvantages.